The problems posed by substances with ozone depletion potential (ODP) were discussed in Montreal, where the protocol was signed requiring a reduction of the production and use of chlorofluorocarbons (CFCs). Amendments were made to this protocol, which imposed abandonment of CFCs, and extended the regulations to cover other products, including hydrochloro-fluorocarbons (HCFCs).
The refrigeration and air conditioning industry has made a considerable investment in the replacement of these refrigerants, which is what led to the marketing of hydrofluorocarbons (HFCs).
The (hydro)chlorofluorocarbons used as expanding agents or solvents have also been replaced with HFCs.
In the automobile industry, the systems for air conditioning of vehicles marketed in many countries have changed over from a chlorofluorocarbon refrigerant (CFC-12) to a hydrofluorocarbon refrigerant (1,1,1,2-tetrafluoroethane: HFC-134a), which is less harmful to the ozone layer. However, with regard to the objectives established by the Kyoto protocol, HFC-134a (GWP=1300) is considered to have a high warming power. A fluid's contribution to the greenhouse effect is quantified by a criterion, GWP (Global Warming Potential), which summarizes the warming power, taking a reference value of 1 for carbon dioxide.
Carbon dioxide, being nontoxic, nonflammable and having a very low GWP, has been proposed as refrigerant for air conditioning systems, replacing HFC-134a. However, the use of carbon dioxide has several drawbacks, notably connected with the very high pressure for application as refrigerant in the existing equipment and technologies.
Moreover, the mixture R-404A consisting of 44 wt. % of pentafluoroethane, 52 wt. % of trifluoroethane and 4 wt. % of HFC-134a is widely used as fluid for refrigeration of large areas (supermarkets) and in refrigerated transport. However, this mixture has a GWP of 3900. The mixture R-407C, consisting of 52 wt. % of HFC-134a, 25 wt. % of pentafluoroethane and 23 wt. % of difluoromethane, is used as heat transfer fluid in air conditioning and heat pumps. However, this mixture has a GWP of 1800.
Document JP 4110388 describes the use of hydrofluoropropenes of formula C3HmFn, with m, n representing an integer between 1 and 5 inclusive and m+n=6, as heat transfer fluids, in particular tetrafluoropropene and trifluoropropene.
Document WO2004/037913 discloses the use of compositions comprising at least one fluoroalkene having three or four carbon atoms, notably pentafluoropropene and tetrafluoropropene, preferably having a GWP of at most 150, as heat transfer fluids.
Document WO 2005/105947 teaches the addition to tetrafluoropropene, preferably 1,3,3,3-tetrafluoropropene, of a co-blowing agent such as difluoromethane, pentafluoroethane, tetrafluoroethane, difluoroethane, heptafluoropropane, hexafluoropropane, pentafluoropropane, pentafluorobutane, water and carbon dioxide.
Document WO 2006/094303 discloses an azeotropic composition containing 7.4 wt. % of 2,3,3,3-tetrafluoropropene (1234yf) and 92.6 wt. % of difluoromethane (HFC-32). This document also discloses an azeotropic composition containing 91 wt. % of 2,3,3,3-tetrafluoropropene and 9 wt. % of difluoroethane (HFC-152a).
A heat exchanger is a device enabling thermal energy to be transferred from one fluid to another, without mixing them. The thermal flux passes through the exchange surface that separates the fluids. This method is most often used for cooling or heating a liquid or a gas that it is impossible to cool or heat directly.
In compression systems, heat exchange between the refrigerant and the heat sources is effected via heat-transfer fluids. These heat-transfer fluids are in the gaseous state (the air in air conditioning and direct-expansion refrigeration), liquid (the water in domestic heat pumps, glycol solution) or two-phase.
There are various transfer modes:                the two fluids are arranged in parallel and go in the same sense: co-current mode (antimethodical);        the two fluids are arranged in parallel but go in the opposite sense: countercurrent mode (methodical);        the two fluids are positioned perpendicularly: crossed-current mode. Crossed-current can have a co-current or countercurrent tendency;        one of the two fluids makes a U-turn in a wider pipeline, which the second fluid passes through. This configuration is comparable to a co-current exchanger over half its length, and to a countercurrent exchanger for the other half: pin-head mode.        